I used a 22mm pvc pipe attached to a garden hose to tunnel under a 2.5 metre section of patio for my garden irrigation system. I plan to use the pipe as a conduit, I'll put my irrigation hose pipe through this pipe.

Items Used:
Pushfit 22mm Overflow Pipe PVCU 3m - £1.50 (Selco)
Hozelock Round Mixer Tap Connector(maximum of 24mm diameter) - £5.37 (Amazon)